Support for long channel length nanowire transistors

ABSTRACT

A nanowire device includes a first component formed on a substrate and a second component disposed apart from the first component on the substrate. A nanowire is configured to connect the first component to the second component. An anchor pad is formed along a span of the nanowire and configured to support the nanowire along the span to prevent sagging.

BACKGROUND

Technical Field

The present invention relates to semiconductor devices, and moreparticularly to nanowire devices having a long channel length withreduced sagging.

Description of the Related Art

Nanowire field effect transistors (FETs) may be employed for a number ofapplications. Nanowire FETs may be subject to physical degradation dueto mechanical changes, such as sagging. Specifically, in gate all-aroundstructures, long channel devices include long unsupported spans thattend to sag or otherwise deflect either immediately or over time. Thisdeflection can cause the nanowire to touch the substrate or othercomponents, resulting in an undesired result or short. Long lengths ofnanowire can cause mechanical sagging and therefore a lack of structuralintegrity.

SUMMARY

A nanowire device includes a first component formed on a substrate and asecond component disposed apart from the first component on thesubstrate. A nanowire is configured to connect the first component tothe second component. An anchor pad is formed along a span of thenanowire and configured to support the nanowire along the span toprevent sagging.

Another nanowire device includes a source and a drain formed on asubstrate and separated by a span. At least one nanowire is suspendedover the substrate and is configured to connect the source and the drainas a device channel. A gate dielectric and a gate metal are formedaround the at least one nanowire. An anchor pad is formed along the spanand configured to support the at least one nanowire along the span toprevent sagging.

A method for supporting a nanowire device channel includes connecting asource to a drain using at least one nanowire as a device channel; andsupporting the at least one nanowire with an anchor pad formed along aspan of the at least one nanowire and configured to support the at leastone nanowire along the span to prevent sagging.

These and other features and advantages will become apparent from thefollowing detailed description of illustrative embodiments thereof,which is to be read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The disclosure will provide details in the following description ofpreferred embodiments with reference to the following figures wherein:

FIG. 1 is a partial top view of a semiconductor device showing ananowire device channel being supported by anchor pads between twocomponents (e.g., a source region and a drain region of thesemiconductor device) in accordance with the present principles;

FIG. 2 is a cross-sectional view taken at section line 2-2 of FIG. 1showing the nanowires having a gate all-around structure in accordancewith on embodiment in accordance with the present principles;

FIG. 3 is a cross-sectional view taken at section line 3-3 of FIG. 1showing anchor pads anchored to a dielectric layer formed on a substratein accordance with one illustrative embodiment in accordance with thepresent principles;

FIG. 4 is a block/flow diagram showing a method for supporting nanowiresin accordance with one illustrative embodiment; and

FIG. 5 is a partial op view of a semiconductor device showing a nanowiredevice channel having a nanowire including nanowire segments and beingsupported by anchor pads between two regions (e.g., a source region anda drain region of the semiconductor device), in accordance with thepresent principles.

DETAILED DESCRIPTION

In accordance with the present principles, nanowires and methods forformation of nanowires are provided. The nanowires include anchor padsdisposed between sections or segments of nanowires to prevent nanowiresagging. The anchor pads may vary in size and number, and may be placedat different distances along the nanowire(s). The anchor pads arepreferably integrally formed with the nanowires, and preferably includethe same materials and are formed in a same formation process. Truenanowire current can be computed by subtracting out the influences ofthe anchor pads based pad width(s) of the anchor pads to extract currentas though the anchor pads were not present.

The nanowires described herein include gate all-around nanowires. Itshould be understood that the nanowires may have other structures andconfigurations. For example, the nanowires may be included as a devicechannel for a nanowire transistor but may also be employed as conductivelines. In addition, the nanowires may include a number of differentshaped cross-sections, for example, square or rectangular shapes as wellas the circular or round shapes as described herein. The overall lengthof the nanowire or cumulative segments of the nanowires is determined inaccordance with a particular application, and in accordance with thepresent principles is no longer limited by limitations arising fromunsupported length on the nanowires.

It is to be understood that the present invention will be described interms of a given illustrative architecture; however, otherarchitectures, structures, substrate materials and process features andsteps may be varied within the scope of the present invention.

It will also be understood that when an element such as a layer, regionor substrate is referred to as being “on” or “over” another element, itcan be directly on the other element or intervening elements may also bepresent. In contrast, when an element is referred to as being “directlyon” or “directly over” another element, there are no interveningelements present. It will also be understood that when an element isreferred to as being “connected” or “coupled” to another element, it canbe directly connected or coupled to the other element or interveningelements may be present. In contrast, when an element is referred to asbeing “directly connected” or “directly coupled” to another element,there are no intervening elements present.

A design for an integrated circuit chip may be created in a graphicalcomputer programming language, and stored in a computer storage medium(such as a disk, tape, physical hard drive, or virtual hard drive suchas in a storage access network). If the designer does not fabricatechips or the photolithographic masks used to fabricate chips, thedesigner may transmit the resulting design by physical means (e.g., byproviding a copy of the storage medium storing the design) orelectronically (e.g., through the Internet) to such entities, directlyor indirectly. The stored design is then converted into the appropriateformat (e.g., GDSII) for the fabrication of photolithographic masks,which typically include multiple copies of the chip design in questionthat are to be formed on a wafer. The photolithographic masks areutilized to define areas of the wafer (and/or the layers thereon) to beetched or otherwise processed.

Methods as described herein may be used in the fabrication of integratedcircuit chips. The resulting integrated circuit chips can be distributedby the fabricator in raw wafer form (that is, as a single wafer that hasmultiple unpackaged chips), as a bare die, or in a packaged form. In thelatter case the chip is mounted in a single chip package (such as aplastic carrier, with leads that are affixed to a motherboard or otherhigher level carrier) or in a multichip package (such as a ceramiccarrier that has either or both surface interconnections or buriedinterconnections). In any case the chip is then integrated with otherchips, discrete circuit elements, and/or other signal processing devicesas part of either (a) an intermediate product, such as a motherboard, or(b) an end product. The end product can be any product that includesintegrated circuit chips, ranging from toys and other low-endapplications to advanced computer products having a display, a keyboardor other input device, and a central processor.

It should also be understood that material compounds will be describedin terms of listed elements, e.g., InGaAs or SiGe. These compoundsinclude different proportions of the elements within the compound, e.g.,SiGe includes Si_(x)Ge_(1-x) where x is less than or equal to 1, etc. Inaddition, other elements may be included in the compound and stillfunction in accordance with the present principles. The compounds withadditional elements will be referred to herein as alloys.

Reference in the specification to “one embodiment” or “an embodiment” ofthe present principles, as well as other variations thereof, means thata particular feature, structure, characteristic, and so forth describedin connection with the embodiment is included in at least one embodimentof the present principles. Thus, the appearances of the phrase “in oneembodiment” or “in an embodiment”, as well any other variations,appearing in various places throughout the specification are notnecessarily all referring to the same embodiment.

It is to be appreciated that the use of any of the following “/”,“and/or”, and “at least one of”, for example, in the cases of “A/B”, “Aand/or B” and “at least one of A and B”, is intended to encompass theselection of the first listed option (A) only, or the selection of thesecond listed option (B) only, or the selection of both options (A andB). As a further example, in the cases of “A, B, and/or C” and “at leastone of A, B, and C”, such phrasing is intended to encompass theselection of the first listed option (A) only, or the selection of thesecond listed option (B) only, or the selection of the third listedoption (C) only, or the selection of the first and the second listedoptions (A and B) only, or the selection of the first and third listedoptions (A and C) only, or the selection of the second and third listedoptions (B and C) only, or the selection of all three options (A and Band C). This may be extended, as readily apparent by one of ordinaryskill in this and related arts, for as many items listed.

Referring now to the drawings in which like numerals represent the sameor similar elements and initially to FIG. 1, a partial top view of asemiconductor device including nanowire field effect transistors (FETs)10 is illustratively shown. The ITT 10 is formed on a substrate 15,which may include dielectric layers, other FETs, conductors and otherstructures for the semiconductor device. The substrate 15 may include amonocrystalline substrate and may include a bulk substrate or asemiconductor-on-insulator substrate. The substrate may include anysuitable substrate material, such as, e.g., Si, SiGe, SiC, Ge, III-Vmaterials, etc.

The FET 10 includes a source 12, a drain 14 and a composite gatestructure/region 16. The composite gate structure 16 is a region that isschematically depicted to show a spatial relationship with the othercomponents. The composite gate structure 16 represents gate dielectricand gate metal as will be described with reference to FIG. 2. The box 16depicted in FIG. 1 represents any suitable gate structure, such as,e.g., a gate all-around structure, a gate layer or plate above or belowthe nanowires 22, etc.

In a gate all-around structure, the gate dielectric and gate metal areformed annularly or otherwise encapsulating the nanowires 22. In otherembodiments, the gate metal or conductor may include a plate inproximity of the nanowires 22 with or without a dielectric layerdisposed between the nanowires 22 and the gate metal or conductor.

The gate region 16 connects to a gate line 18 by conductive lines 20.The nanowires 22 are suspended over the substrate 15 on which the device10 is formed. The substrate 15 may include a semiconductor substrate,such as Si, although other materials may be employed, e.g., glass,quartz, ceramic, etc. Other layers (32, FIG. 2) may be provided betweenthe substrate 15 and the nanowires 22. The conductive lines 20 may beconnected to the gate line 18 by vias 26. In addition the nanowires 22may be connected to the source 12 and the drain using vias 26. It shouldbe understood that other multiple layer configurations and structuresmay be employed in addition to or instead of the structuresillustratively shown.

The source 12 and drain 14 may have their positions interchanged. Thesource 12 and drain 14 may include doped semiconductor regions,conductive metals, or any other conducting components.

Nanowires 22 described herein refer to material forming a devicechannel. Nanowires 22 form the device channel for the FET 10. Thenanowires 22 may include a diameter or width of between about 5 nm andabout 100 nm.

Being the device channel, the nanowires 22 provide a channel length forthe device 10. The channel length is a distance between the source 12and drain 14. The channel length includes nanowire segments 28 and padwidths 27 of anchor pads 24. In accordance with the present principles,the anchor pads 24 provide support for the nanowire segments 28 andprevent mechanical sagging. The nanowire segments 28 include a nanowiresegment length 29, which may be the same for all segments of the device10 or groups of segments may have different nanowire segment lengths 29for different portions of the device 10.

It should be understood that FIG. 1 illustratively depicts threenanowires 22 connecting two components 12, 14. However, one or more(e.g., greater than three) nanowires 22 may be employed. In addition thesource 12 and drain 14 may include other components or structures, e.g.,nodes connecting to passive elements (e.g., capacitors, etc.) or otheractive components (e.g., diodes, etc.).

Referring to FIG. 2 with continued reference to FIG. 1, the nanowires 22include an appropriately doped semiconducting material, for example, Si,SiGe, Ge, a III-V semiconductor, such as, e.g., GaAs or InGaAs. FIG. 2shows a cross-section taken at section line 2-2 in FIG. 1. The nanowiresegments 28 are surrounded by dielectric material 34 (e.g., a high-Kdielectric material) and a metal gate material 36. If a high-kdielectric material is employed, the high-K dielectric material 34 mayinclude, e.g., hafnium oxide, although other materials may be employed.The metal gate material 36 may include, e.g., tungsten, although othergate materials may be employed. The metal gate material 36 isrepresented as part of the composite gate region 16 in FIG. 1. The metalgate material 36 connects to the conductive lines 20 through, e.g., viasor other connections (not shown). In other embodiments, the metal gatematerial 36 may include another dielectric material (not shown) formedon it.

In particularly useful embodiments, the nanowire segments 28 may includea nanowire segment length 29 of between about 50 nm to about 300 run andpreferably between about 100 nm to about 200 nm. The overall channellength including the widths of the anchor pads 24 and of all thenanowire segments 28 may be between about 500 nm to about 2 microns. Itshould be understood that while the FIGS. show three nanowires 22, thepresent principles are applicable to devices with a single nanowire ormultiple parallel nanowires.

Referring to FIG. 3, with continued reference to FIG. 1, FIG. 3 shows across-section taken at section line 3-3 in FIG. 1. The nanowires 22 aremounted to the anchor pads 24 in a periodic manner. The anchor pads 24are anchored to the substrate 15 or layers 32 formed on the substrate15. The anchor pads 24 are depicted as rectangular; however, it shouldbe understood that the anchor pads 24 may include any shape, e.g., oval,round, polygonal, etc. The anchor pads 24 are preferably integrallyformed with the nanowires 22, and are composed of a same material andare formed at the same time.

A dielectric layer 40 or protective layer may be formed over the anchorpads 24. The dielectric layer 40 may include an oxide, a nitride orother suitable material.

In such a case, the anchor pads 24 may need to be exposed to a voltageto enable conduction, A gate plate may be employed to provide this(e.g., gate region 16, FIG. 1). In this way, a gate metal may be formedcorresponding to a shape of the anchor pad 24 or may include the entireregion 16. The gate metal may be formed over or under the anchor pad 24with a gate dielectric formed therebetween. Alternatively, the largerarea provided by the anchor pads 24 may provide sufficient conductionwithout the need for gate activation for conduction. Narrow geometry ofthe nanowire 22 contrasts with the wide geometry of the anchor pads 24and is what causes the nanowire 22 to become suspended, While the anchorpad 24 remains anchored (i.e., does not become suspended).

The anchor pads 24 enable long gate length devices using nanowires 22.In the conventional art, the long nanowires (which are required tocreate long channel transistors) tend to sag, which compromises thestructural integrity of the nanowire and thus negatively affectstransistor performance. In accordance with the present principles, longnanowires 22 made even longer using anchor pads 24. The nanowiresegments 28 are periodically anchored to the substrate 15 along thelength of the channel by anchor pads 24. This preserves the structuralintegrity of the nanowires 22 by preventing sagging.

In particularly useful embodiments, the anchor pads 24 may include a padwidth of between about 20 nm to about 50 nm. The thickness of the anchorpads 24 may be between about 50 nm to about 500 nm. The anchor pads 24may include a thickness of between two to five times thediameter/thickness of the nanowires 22. The anchor pads 24 may beperiodically provided after a nanowire segment length of about 200 nm,although anchors shapes 24 may be placed after segment lengths havingother dimensions.

The nanowires 22 and anchor pads 24 can be formed using lithographicprocessing. This includes nanowire and pad patterning and lithographyusing a photolithography mask, followed by a nanowire and pad etch usinga reactive ion etch (RIE) or other etch process. Next, a nanowirerelease etch is performed using another etch process to free thenanowire segments 28 from the substrate 15. After this, a gate-first orreplacement metal gate processing continues as is known in the art.

Referring to FIG. 4, a method for supporting a nanowire device channelis illustratively shown. In some alternative implementations, thefunctions noted in the blocks may occur out of the order noted in thefigures. For example, two blocks shown in succession may, in fact, beexecuted substantially concurrently, or the blocks may sometimes beexecuted in the reverse order, depending upon the functionalityinvolved. It will also be noted that each block of the block diagramsand/or flowchart illustration, and combinations of blocks in the blockdiagrams and/or flowchart illustration, can be implemented by specialpurpose hardware-based systems that perform the specified functions oracts or carry out combinations of special purpose hardware and computerinstructions.

It should be further noted that the processing needed to form thenanowire transistor devices in accordance with the present principlesmay include known semiconductor processing techniques. For example, thesource and drain regions may be formed by doping areas of a substrate,or epitaxially growing (and doping) areas of the substrate to formsource and drain regions. In addition, patterned etching may be employedto form the nanowires and the anchor pads. Deposition and patterning maybe employed to form metal connection and dielectric layers, as needed.

In block 80, a source is connected to a drain using at least onenanowire as a device channel. This may be performed using connectionstructures, such as vias or contacts. In block 82, the at least onenanowire is supported by an anchor pad formed along a span of the atleast one nanowire and configured to support the at least one nanowirealong the span to prevent sagging.

In one embodiment, the nanowire, including, nanowire segments 28 and theanchor pads 24, may be grown or deposited on the substrate (or otherlayers). A first etch shapes (or patterns) the anchor pads and thenanowires, then the anchor pads are covered and a second etch etches thenanowires to further reduce the nanowires and remove contact with thesubstrate. This causes the nanowires to be suspended. In accordance withthe present principles the nanowires are suspended between the anchorpads.

FIG. 5 is a partial top view of a semiconductor device showing ananowire device channel having a nanowire including nanowire segmentsand being supported by anchor pads between two regions (e.g., a sourceregion and a drain region of the semiconductor device), as described forFIG. 1, in accordance with the present principles.

Having described preferred embodiments for support for long channellength nanowire transistors (which are intended to be illustrative andnot limiting), it is noted that modifications and variations can be madeby persons skilled in the art in light of the above teachings. It istherefore to be understood that changes may be made in the particularembodiments disclosed which are within the scope of the invention asoutlined by the appended claims. Having thus described aspects of theinvention, with the details and particularity required by the patentlaws, what is claimed and desired protected by Letters Patent is setforth in the appended claims:

The invention claimed is:
 1. A method for supporting a nanowire devicechannel, comprising: connecting a source to a drain using at least onenanowire as a device channel, wherein each of the at least one nanowireincludes at least two nanowire segments and at least one interveninganchor pad; and supporting the at least one nanowire with the at leastone intervening anchor pad formed along a span of the at least onenanowire, wherein the intervening anchor pad has a width in the range ofabout 20 nm to about 50 nm.
 2. The method of claim 1, wherein each ofthe at least two nanowire segments is suspended over a substrate onwhich the source and drain are formed.
 3. The method as recited in claim2, wherein supporting the at least two nanowire segments with the atleast one intervening anchor pad includes supporting at least threenanowire segments with a plurality of anchor pads disposed along thespan with a periodicity of about 200 nm.
 4. The method of claim 3,further comprising forming a dielectric layer over the plurality ofanchor pads.
 5. The method of claim 3, wherein each of the plurality ofanchor pads has a thickness in the range of about 50 nm to about 500 nm.6. The method of claim 1, wherein the at least one nanowire is formed bya lithographic process including patterning, and a release etch, thatfrees the nanowire segments of the at least one nanowire from thesubstrate.
 7. The method of claim 1, wherein a plurality of nanowiresconnect the source to the drain.
 8. The method of claim 1, wherein theat least one nanowire has a length in the range of about 500 nm to 2microns.
 9. The method of claim 8, wherein the at least two nanowiresegments each have a length in the range of about 50 am to about 300 nm.10. The method of claim 9, wherein a plurality of anchor pads support atleast three nanowire segments for each of the at least one nanowire, andthe plurality of anchor pads are disposed along the device channel witha periodicity equal to the nanowire segments length, such that each ofthe at least three nanowire segments is supported by at least one anchorpad.
 11. A method of forming a nanowire device, comprising: forming atleast one nanowire, including a plurality of anchor pads and a pluralityof nanowire segments along a span of the at least one nanowire, wherethe at least one nanowire is configured to connect a first region to asecond region, wherein each of the plurality of anchor pads has a widthin the range of about 20 nm to about 50 nm, and wherein the plurality ofanchor pads are disposed along the span with a periodicity of about 200nm and are configured to support the plurality of nanowire segmentsalong the span to prevent sagging.
 12. The method of claim 11, whereinat least a first anchor pad has a first size and at least a secondanchor pad has a second size different than the first anchor pad size.13. The method of claim 11, wherein a plurality of nanowires connectsthe first region to the second region, and at least one of the pluralityof nanowire segments has a first length different from a second lengthof another nanowire segment.
 14. The method of claim 13, wherein atleast one of the anchor pads is placed a distance from the first regionor the second region equal to the first length of the at least one ofthe plurality of nanowire segments.
 15. The method of claim 13, whereinthe plurality of nanowire segments has a square cross-section.
 16. Themethod of claim 13, wherein each of the plurality of nanowire segmentsis surrounded by a high-K dielectric material.
 17. A method of forming ananowire device, comprising: forming a source and a drain on asubstrate, where the source and drain are separated by a span; formingat least one nanowire configured to connect the source and the drain asa device channel, wherein the at least one nanowire includes a pluralityof anchor pads, configured to support the at least one nanowire, whereineach of the plurality of anchor pads has a width in the range of about20 nm to about 50 nm.
 18. The method of claim 17, wherein the at leastone nanowire includes a plurality of nanowire segments having a circularcross-section with a diameter between about 5 nm and about 100 nm. 19.The method of claim 17, wherein each of the plurality of anchor pads hasa thickness in the range of about 50 nm to about 500 nm.
 20. The methodof claim 19, wherein the plurality of anchor pads are disposed along thespan with a periodicity of about 200 nm.